VARIANT INSULIN-LIKE GROWTH FACTOR I RECEPTOR SUBUNITS AND METHODS FOR USE THEREOF

Abstract: The present invention provides novel IGF-I receptor subunits characterized by modified IGF-I receptor function, novel polynucleic acid sequences that encode these receptor subunits, and various applications for their use.

Description: VARIANT INSULIN-LIKE GROWTH FACTOR I RECEPTOR SUBUNITS AND METHODS FOR USE THEREOF , ACKNOWLEDGEMENT The invention was made with Government support under Grant Numbers DK34824 and DK02023, awarded by the National Institute of Health. The Government may have certain rights in the invention. FIELD OF THE INVENTION The present invention relates to insulin-like growth factor-I and its receptor, and more particularly relates to insulin-like growth factor-I receptor subunits and receptors having modified tyrosine kinase activity, as well as methods for use thereof. BACKGROUND OF THE INVENTION Insulin-like growth factor (IGF-I) is a 7.5-kD polypeptide that circulates in plasma in high concentrations and is detectable in most tissues. IGF-I is predominantly a mitogenic factor for a variety of cell and tissue types, but also stimulates cell differentiation and cell proliferation. The importance of IGF-I to growth of tissues is suggested by increasing plasma concentrations throughout adolescence, reaching a plateau in adults, and in the requirement of most mammalian cell types for IGF-I for sustained proliferation. For a review of the wide variety of cell types for which IGF-I/IGF-I receptor interaction mediates cell proliferation, see Goldring, M.B. and Goldring, S.R.., Eukar. Gene Expression. 1:31-326 (1991). In vivo, serum levels of IGF-I are dependent on pituitary growth hormone(GH) . Although the liver is a major site of growth hormone-dependent IGF-I synthesis. recent work indicates that the majority of normal tissues also produce IGF-I. A variety of neoplastic tissues may also produce IGF-I. Thus IGF-I may acts as a regulator of normal and abnormal cellular proliferation via autocrine or paracrine, as well as endocrine mechanisms. The first step in the transduction pathway leading to IGF-I-stimulated cellular proliferation is binding of receptor ligand (IGF-I, IGF-II, or insulin at supraphysiological concentrations) to IGF-I receptor. The IGF-I receptor is composed of two types of subunits: an alpha subunit (a 130-135kD protein that is entirely extracellular and functions in ligand binding) and a beta subunit (a 95-kD transmembrane protein, with transmembrane and cytoplasmic domains) . The IGF-I receptor is initially synthesized as a single chain proreceptor polypeptide which is processed by glycosylation, proteolytic cleavage, and covalent bonding to assemble into a mature 460-kD heterotetramer comprising two alpha-subunits and two beta-subunits. The beta subunit(s) possesses ligand-activated tyrosine kinase activity. This activity is implicated in the signaling pathways mediating ligand action which involve autophosphorylation of the beta-subunit and phosphorylation of IGF-I receptor substrates. Thus the IGF-I receptor is seen to play a pivotal role in normal and abnormal proliferative processes. Enhanced IGF-I levels are correlated with several, diverse pathological states, including acromegaly, gigantism. Abnormal IGF-I/IGF-I receptor function has been implicated in psoriasis, diabetes (microvascular proliferation) , smooth muscle restenosis of blood vessels following angioplasty. In a variety of cancers, such as leukemia, lung cancer, ovarian cancer and prostate cancer, there is overexpression of the IGF-I receptor by the tumor tissue relative to the non- cancerous tissue, possibly implicating IGF-I/IGF-I receptor interaction in an autocrine or paracrine feedback loop resulting in autonomous proliferation of the tissue. For a review of the role IGF-I/IGF-I receptor interaction plays in the growth of a variety of human tumors, see Macaulay, V.M. , Br. J. Cancer. 65: 311- 320 (1992). Potential strategies for the inhibition of cell proliferation associated with such pathologies include suppressing IGF-I levels or interrupting IGF-I action at the level of its cellular receptor. For example, drugs have been employed to reduce IGF synthesis and/or secretion. These include the long acting somatostatin analogue octreotide for treatment of endocrine tumors including carcinoid, and experimentally for the treatment of acromegaly and breast cancer, and tamoxifen for the treatment of breast cancer. However, there has been an inherent difficulty in suppressing circulating IGF-I to levels such that tissue concentrations become limiting to cell growth, especially without affecting normal growth of non-targeted tissue. One strategy for interrupting IGF-I action at the level of its cellular receptor employs antibodies to the IGF-I receptor. However, it has been reported that these antibodies can be stimulatory rather than antagonistic over time. There is, therefore, a clear need in the art for methods of modifying ligand activated IGF-I receptor function at the cellular level. Preferably such methods would enable inheritable modifications of IGF-I receptor function in the cells of target tissue without disrupting the endogenous IGF-I receptor function in cells of non-targeted tissue. BRIEF DESCRIPTION OF THE INVENTION The present invention provides novel polynucleic acids comprising a sequence encoding an IGF-I receptor subunit(s) having modified IGF-I receptor function relative to endogenous IGF-I receptor, and the polypeptides encoded thereby. The IGF-I receptor subuni (s) encoded by the polynucleic acids of the present invention may correspond to either the beta subunit or the alpha and beta subunits of the IGF-I receptor. One IGF-I receptor function which may be modified is tyrosine kinase activity. Tyrosine kinase activity includes autophosphorylation and phosphorylation of cytosolic IGF-I receptor substrate, either one, or both of which may be modified in accordance with the present invention. Variant IGF-I receptors provided by the present invention are characterized by modified IGF-I receptor function, for example modified tyrosine kinase activity, relative to endogenous IGF-I receptor, and are typically assembled from at least one variant beta subunit to form a variant IGF-I receptor heterotetramer. Alternatively, variant IGF-I receptor may be assembled from two variant beta subunits. The present invention also provides methods of inhibiting endogenous IGF-I receptor function using the novel polynucleic acids and polypeptides of the present invention. BRIEF DESCRIPTION OF THE FIGURES Fig. 1 is a schematic diagram of the pRSV-IGFIR plasmid used for transfection of target cells. An 4.2 kb Hindi/Sstl fragment of the human IGF-I receptor cDNA was cloned into expression vector Rexp. DETAILED DESCRIPTION OF THE INVENTION The present invention provides novel IGF-I receptor subunits characterized by modified IGF-I receptor function, novel polynucleic acid sequences that encode these receptor subunits, and various applications for their use. The activation of the IGF-I receptor by its ligands plays a central role in the proliferation of a wide variety of cell types and is implicated in the progression of many diseases. Efforts directed to treating diseases associated with high levels of cellular IGF-I have met with limited success as they have focused on either lowering serum concentrations of IGF-I or obstructing IGF-I binding to IGF-I receptor. The present invention avoids the inherent difficulties associated with these strategies and provides a inheritable, tissue- specific method of modifying ligand activated IGF-I receptor function at the cellular level. IGF-I receptor has several functional sites, for example, ligand binding, substrate-binding, autophosphorylation, phosphorylation of substrate, membrane association, binding between the subunits, and so on. Generally speaking, it has been discovered that one or more functions of IGF-I receptor can be independently modified (i.e., by selective mutation of nucleic acid encoding the IGF-I receptor subunit(s) ) without significantly disrupting the other functions of the receptor. Exploiting this phenomenon, variants of endogenous IGF-I receptors may be formed by selectively mutating that portion of a nucleotide sequence which encodes for the function of interest. The resulting variant subunits maintain their ability to complex with either endogenous IGF-I receptor subunits or other variant IGF-I receptor subunits to form variant IGF-I receptors. When the variant IGF-I receptor subunit is present in the target cell, the target cell exhibits the phenotype characteristic of the variant IGF-I receptor subunit in a dominant negative fashion. The phenotype characteristic of the variant subunit and receptor is referred to as "dominant" because it is manifested even in the presence of the endogenous gene. The phenotype of the variant subunit and receptor is referred to as "negative" because it is antagonistic to the phenotype of the endogenous IGF-I receptor. Use of the dominant negative terminology, however, is not intended to exclude the desired phenotype which may result from competition due to the presence of a large number of variant subunits in the cell. Thus, the methods of the present invention employ recombinant nucleic acid technology to express variant IGF-I receptor subunit. Expression of variant subunit exerts a dominant negative effect on endogenous IGF-I receptor subunits and produces the desired phenotype in the targeted cells, as well as their progeny. In accordance with the present invention, there is provided a recombinant polynucleic acid comprising a sequence encoding IGF-I receptor subunit(s) . The encoded IGF-I receptor subunit(s) is characterized by modified IGF-I receptor function relative to the IGF-I receptor function of endogenous IGF-I receptor. The term "polynucleic acid" is intended to include deoxyribonucleic acid and ribonucleic acid in all their forms, i.e., double-stranded DNA, cDNA, mRNA and the like. Polynucleic acid sequences encoding IGF-I receptor subunit(s) may encode none, part or all of the alpha subunit of the IGF-I receptor. In a presently preferred embodiment of the invention, polynucleic acid sequences encode both the alpha and the beta subunits of the IGF-I receptor with appropriate mutations to achieve modified tyrosine kinase activity. The term "IGF-I receptor function" is intended to include IGF-I receptor function associated with both disease and non-diseased states, for example, tyrosine kinase activity, ligand binding, internalization of ligand, ATP binding, binding of cytoplasmic substrate, ligand-dependent cell differentiation, ligand-dependent cell proliferation, ligand-dependent cell transformation, ligand-dependent cell tu origenesis, and the like. The term "ligand-dependent" is used herein to indicate that the IGF-I receptor function is dependent upon binding of ligand to the IGF-I receptor to activate the function. The term "modified" as used to modify "IGF-I receptor function" or "tyrosine kinase activity" or any one of the IGF-I receptor functions, refers to an increase, decrease, change in pattern or absence of that function relative to the function of endogenous IGF-I receptor. As used herein, the term "endogenous IGF-I receptor" is intended to mean IGF-I receptor native to the cell of interest. The term "endogenous IGF-I receptor subunit" as used herein is intended to mean the alpha and/or the beta subunit of the IGF-I receptor native to the cell. In accordance with the present invention, there also provided a recombinant polynucleic acid comprising a sequence encoding IGF-I receptor subunit(s) wherein the encoded IGF-I receptor subunit(s) is characterized by modified tyrosine kinase activity relative to the tyrosine kinase activity of endogenous IGF-I receptor subunit. The term "modified tyrosine kinase activity" as used herein, refers to an increase, decrease, change in pattern or absence of tyrosine kinase activity relative to the tyrosine kinase activity of endogenous IGF-I receptor. The term "tyrosine kinase activity" includes autophosphorylation of the IGF-I receptor and phosphorylation of cytoplasmic substrate i.e., IRS-1, P13 kinase, ppl85, and the like. δ Set forth as SEQ ID NO 1 is a DNA sequence representing a cDNA clone encoding alpha and beta subunits of human IGF-I receptor. Set forth as SEQ ID NO 2 is the deduced amino acid sequence encoded by SEQ ID NO 1. Nucleotides 32 through 121 encode the signal sequence. Nucleotides 122 through 2239, and amino acids 1 through 706 encode the alpha subunit. Nucleotides 2252 through 4132, and amino acids 711 through 1337 encode the beta subunit. The alpha and beta subunits of mature IGF-I receptor are linked by a disulfide bond. With reference to SEQ ID NO 2 this binding site on the beta subunit is within amino acids 744 through about 906. The beta subunit can be further described as having a transmembrane region at or about amino acid residues 906 through about 929 of SEQ ID NO 2. The beta subunit also has a juxta-membrane region adjacent to the transmembrane region at amino acid residues 930 through about 990. When the mature IGF-I receptor is anchored in the cell membrane, the juxta-membrane region is located within the cytosol adjacent to the cell membrane. Further downstream of the juxta-membrane region on the beta subunit is the ATP binding domain at about amino acid residue 1003. Between the ATP binding site and the carboxy terminus at amino acid 1337, lies the cytosolic tyrosine kinase domain at about amino acid residues 973- 1229. In another embodiment of the present invention, the nucleic acid sequence of endogenous IGF-I receptor subunit, or a nucleic acid sequence that is compatible with the target cell and encodes IGF-I receptor subunit, is modified, for example, by mutation such that the expressed IGF-I receptor subunit has modified IGF-I receptor function. Of course, the location chosen for mutation will depend upon the function of the endogenous IGF-I receptor which one desires to modify. The juxta- membrane region, for example at amino acid residues 943, 950 and 957, the ATP binding site, for example at residue 1003, and the cytosolic tyrosine kinase domain, for example, at amino acid residues 1131, 1135 and 1136 and the carboxy terminus at amino acid residue 1316 are all amenable to amino acid substitutions to modify tyrosine kinase activity. In addition, truncation of the beta subunit by insertion of an inframe stop codon (UAG, UAA or UGA) , for example, at amino acid residue 952 of the beta subunit, as well as a 22 amino acid residue deletion of amino acids 943 through 966, results in modified tyrosine kinase activity. Details of the mutations to the beta subunit referenced above are described in greater detail in the Examples provide below. Using the information provided in the present disclosure, one of skill in the art will appreciate that there are many other ways, well known to those of skill in the art, to mutate the nucleic acid sequence, or alter the amino acid sequence to achieve the desired result, including any one of a number of missense or nonsense mutations. In a presently preferred embodiment, only that portion of the beta subunit necessary for binding the alpha subunit to form a mature IGF-I receptor tetramer, and only that portion of the beta subunit necessary to anchor the IGF-I receptor subunit in the cell membrane is encoded by the polynucleic acid sequences and amino acid sequences of the present invention. For example, the nucleic acid sequences and the amino acid sequences may only encode the amino-terminus of the beta subunit through that portion of the transmembrane domain necessary to achieve anchorage, i.e., amino acid residue 2252 through about 2909. The phrase "substantially the same" is used herein in reference to nucleic acid sequences or amino acid sequences that have non-consequential sequence variations from SEQ ID NO 1 and SEQ ID NO 2, respectively, other than those variations necessary to achieve modified IGF-I receptor function in accordance with the present invention. For example, the nucleotide sequences and amino acid sequences resulting from the mutations to human IGF-I receptor cDNA as described in Example II would be substantially the same as SEQ ID NO 1. Likewise, the amino acid sequences resulting from expression of these mutant human IGF-I receptor cDNA would be substantially the same as SEQ ID NO 2. Similarly, changes in nucleotide sequences or amino acid sequences that result in substitution of a charged residue for a similarly charged residue or substitution of a non-polar residue for another non-polar residue that does not substantially alter the function of the IGF-I receptor subunit (except as provided above) or its tertiary structure would be "substantially the same" sequence. In yet another embodiment of the present invention there is provided a polynucleic acid comprising a sequence encoding an IGF-I receptor subunit characterized by modified IGF-I receptor function, for example, modified tyrosine kinase activity, relative to endogenous IGF-I receptor function, and further characterized by its ability to complex with endogenous IGF-I receptor subunit(s) to form variant IGF-I receptors. The term "variant IGF-I receptor" as used herein refers to a mature IGF-I receptor having a tetrameric structure comprised of two alpha subunits and two beta subunits, wherein at least one of the beta subunits is a variant IGF-I receptor subunit and the receptor has a desired dominant phenotype, usually antagonistic to the phenotype of the endogenous IGF-I receptor. The term "variant IGF-I receptor subunit" as used herein is intended to mean an IGF-I receptor subunit exhibiting modified IGF-I receptor function relative to endogenous IGF-I receptor function, when the variant IGF-I receptor subunit is a constituent of the variant IGF-I receptor. For example, a variant IGF-I receptor subunit may exhibit modified tyrosine kinase activity relative to endogenous IGF-I receptor subunit. A variant IGF-I receptor subunit may be further characterized by its ability to complex with endogenous IGF-I receptor subunit(s) to form a variant IGF-I receptor. In still another embodiment of the present invention, there are provided vectors containing the nucleic acids of the present invention. As used herein, "vector" or "plasmid" refers to discrete elements that are used to introduce polynucleic acid sequences of the present invention into cells for either expression or replication. Selection and use of such vectors are well known to those of skill in the art and will vary in accordance with the cell targeted to receive the polynucleic acid. An expression vector includes constructs capable of expressing polynucleic acid sequences that are operatively linked with regulatory sequences, such as promoter regions. Thus, an "expression vector" refers to a recombinant DNA or RNA construct, such as a plasmid, a phage, recombinant virus or other vector that, upon introduction into an appropriate host cell, results in expression of the cloned polynucleic acid sequence. Appropriate expression vectors are well known to those of skill in the art and include those that are replicable in eukaryotic cells and/or prokaryotic cells and those that remain episomal or those which integrate into the host cell genome. Presently preferred plas ids for expression of variant IGF-I receptor subunits in eukaryotic host cells, particularly mammalian cells, include Rexp with an RSV LTR, Moloney murine leukemia virus LTR driven expression vector, and the like. As used herein, a promoter region refers to a segment of polynucleic acid that controls transcription of DNA to which it is operatively linked. The promoter region includes specific sequences that are sufficient for RNA polymerase recognition, binding and transcription initiation. This portion of the promoter region is referred to as the promoter. In addition, the promoter region includes sequences that modulate this recognition, binding and transcription initiation activity of RNA polymerase. Promoters, depending upon the nature of the regulation, may be constitutive or regulated. For example, promoters contemplated for use in the practice of the present invention include the SV40 early promoter, the cyto egalovirus (CMV) promoter, Moloney murine leukemia virus (MMLV) promoter, thymidine kinase promoter, Rous sarcoma virus promoter (RSV) , and the like. As used herein, the term "operatively linked" refers to the functional relationship of polynucleic acid sequences with regulatory and effector sequences of nucleotides, such as promoters, enhancers, transcriptional and translational stop sites, and other signal sequences. For example, operative linkage of DNA to a promoter refers to the physical and functional relationship between the DNA and the promoter such that the transcription of such DNA is initiated from the promoter by an RNA polymerase that specifically recognizes, binds to and transcribes the DNA. In accordance with another embodiment of the present invention, there are provided cells containing the above-described polynucleic acids. Such host cells as bacterial, yeast and mammalian cells can be used for replicating polynucleic acids of the present invention and producing variant IGF-I receptor subunit(s) . Incorporation of cloned polynucleic acid into a suitable expression vector, transfection of eukaryotic cells with a plasmid vector or a combination of plasmid vectors or with linear DNA, or infection with retroviral constructs, and selection of transfected or infected cells are well known in the art (see, Sambrook et al. Molecular Cloning: A Laboratory Manual. Second Edition, Cold Spring Harbor (1989) . Heterologous DNA may be introduced into host cells by any method known to those of skill, in the art, such as transfection with a vector encoding the heterologous DNA by CaP0 4 precipitation (See, e.g., Kashanchi, F., et al. Nucleic Acids Research. 20:4673- 4674 (1992) . This same method can be used to introduce the proteins of the present invention into host cells.) Recombinant cells can then be cultured under conditions whereby the subunit(s) encoded by the DNA is expressed. Preferred cells include mammalian cells, such as for example, tumor cells, lymphocytes, stem cells, pituitary cells, bone marrow cells, fibroblasts and the like. In yet another embodiment of the present invention there are provided polypeptides encoded by the nucleic acids of the present invention. As used herein, the words "protein", "peptide" and "polypeptide" are considered to be equivalent terms and are used interchangeably. In addition to polynucleic acids and protein compositions of matter, several novel methods of using the polynucleic acids and polypeptides of the present invention are provided. The present invention provides methods inhibiting endogenous IGF-I receptor function in a cell by introducing into the cell, variant IGF-I receptor subunit under conditions suitable to form a variant IGF-I receptor, wherein said variant receptor is characterized by modified tyrosine kinase activity relative to endogenous IGF-I receptor tyrosine kinase activity. In will be understood that the methods of the present invention may be performed in vitro, as well. In accordance with the methods of the present invention, the nucleic acid sequences encoding variant IGF-I receptor subunit can be administered to mammals as a therapeutic agent by any means known to those of skill in the art, including intraperitoneal, subcutaneous, intravascular, intramuscular, intranasal or intravenous injection, implant or transdermal modes of administration, and the like. One of skill in the art will appreciate that when the compositions of the present invention are administered as therapeutic agents, it may be necessary to combine the compositions with a suitable pharmaceutical carrier. The choice of pharmaceutical carrier and the preparation of the composition as a therapeutic agent will depend on the intended use and mode of administration. Suitable formulations and methods of administration of therapeutic agents can be readily be determined by one of skill in the art. The dosage regimen for treating IGF-I associated disorders depends on a variety of factors, including type of disorder, age, weight, sex and medical condition of the patient, as well as the severity of the pathology, the route of administration, and the type of therapeutic agent used. A skilled physician or veterinarian can readily determine and prescribe the effective amount of the compound or pharmaceutical required to treat the patient. Conventionally, one of skill in the art would employ relatively low doses initially and subsequently increase the dose until a maximum response is obtained. Because the nucleic acids of the present invention are susceptible to amplification, much lower doses are believed to be effective than with conventional methods of administering drugs. The invention will now be described in greater detail by reference to the following non-limiting examples. EXAMPLE I Plasmid Construction Standard techniques for DNA manipulations as described by Sambrook J. et al., Molecular Cloning - A Laboratory Manual. Second Edition, Cold Spring Harbor (1989) were used for all plasmid constructions. The 4.2- kb cDNA fragment encoding human IGF-I receptor used in the following examples was obtained by screening a human HeLa cell cDNA library (Stratagene, La Jolla, CA) with a DNA fragment of SEQ ID NO 1 (nucleic acid residues 43 through 280) and an oligonucleotide probe as described in Ullrich A., et al. EMBOJ, 5:2503-2512 (1986) and set forth in SEQ ID NO 14. This oligonucleotide was synthesized on an ABI #394 DNA Synthesizer (Applied Biosystems, Inc. Foster City, CA) . Specific clones were selected by three rounds of sequence specific colony hybridization with 32 P-labelled oligonucleotide and DNA fragment probes. Overlapping clones were ligated together to yield a full length clone whose identity was confirmed by DNA sequencing. Expression constructs were prepared by ligating the 4.2-kb Hincll-SstI fragment of the isolated human IGF-I receptor cDNA into the polylinker site of the mammalian expression vector Rexp (See. Fig. 1) . Rexp is described in Yamasaki, H. et al., Mol. Endocrinology 5:890 (1991) and was obtained from M. Rosenfeld, at the University of California, San Diego, CA. A construct in the forward orientation was identified by restriction mapping and was designated pRSV-IGFIR. A construct in the reverse orientation, generated by ligating the BamHl fragment of the human IGF-I receptor cDNA into BamHl site of Rexp expression vector was designated pRSV-rlGFIR. All plasmids were purified over two cesium chloride gradients. EXAMPLE II Mutagenesis of the Human IGF-I Receptor cDNA A 0.45 kb Smal-Hindlll fragment from pRSV-IGFIR was subcloned into M13mpl9. The following primers were utilized for mutagenesis, -CTGGGGAATGCTGTGCTGTAT-3' ( 940 Gly→ 940 Ala; SEQ ID NO 3), -AATGGAGTGCTAGCTGCCTCTGTG-3' ( 943 Tyr→ 943 Ala; SEQ ID NO 4), -AACCCGGAGTGTTTCAGCGCT-3' 950: Tyr→ Cys SEQ ID NO 5) , -AACCCGGAGTCATTCAGCGCT-3' 50 Tyr→ 950 Ser SEQ ID NO 6) , '-AACCCGGAGGCTTTCAGCGCT-3' ?50 Tyr→ 950 Al a SEQ ID NO 7) , -AACCCGGAGCTATTCAGCGCT-3' 950 Tyr→ 950 Leu SEQ ID NO 8) , '-AACCCGGAGACATTCAGCGCT-3' 950 Tyr→ 950 τhr SEQ ID NO 9) , '-GCTGATGTGGCTGTTCCTGAT-3' 57 Tyr→ 95 Al a SEQ ID NO 10) , '-GTGGCCATTGCTACAGTGAAC-3' 1003 Lys→ 1003 Ala ; SEQ ID NO 11) , and 5'-GGGAATGGAGTGCTGTATCGGGAGAAGATCACCATGAGC-3' (22 amino acid deletion; SEQ ID NO 12) . Mutagenizing oligonucleotides were annealed to single-stranded DNA, and subsequent mutagenesis was performed utilizing an Amersham kit according to the manufacturer's instructions. A Sail linker (5'-GTCGAC- 3') was inserted into the Seal site of Smal-Hindlll fragment encoding the IGF-I receptor, producing IGFIR-CRH which contains three additional amino acids (Cys-Arg-His) inserted at position 950. For truncation of the human IGF-I receptor, the 0.45 kb Sma-Hindlll fragment was subcloned into M13mpl9. An Xba linker, 5'TGCTCTAGAGCA3' (SEQ ID NO 13) was inserted into the Seal site present in a Smal-Hindlll IGF-I receptor cDNA fragment, producing an in-frame stop codon at position 952. After reintroduction of the mutant sequences into the pRSV-IGFIR vector, all constructs were subjected to dideoxy sequencing utilizing T7 sequenase (U.S. Biochemical, Cleveland, Ohio) to confirm the mutant sequences. Plasmids containing cDNA encoding the following wild type and the following variant IGF-I receptor subunits were formed: WT = human IGF-I receptor subunit without mutation; 940 Ala = human IGF-I receptor subunit with alanine substitution at residue 940 in the juxta-membrane region; 943 Ala = human IGF-I receptor subunit with alanine substitution at residue 943 in the juxta-membrane region; 950 Cys = human IGF-I receptor subunit with cysteine substitution at residue 950 in the juxta-membrane region; 950 Ser = human IGF-I receptor subunit with serine substitution at residue 950 in the juxta-membrane region; 950 Leu •= human IGF-I receptor subunit with leucine substitution at residue 950 in the juxta-membrane region; 950, Thr = human IGF-I receptor subunit with threonine at residue 950 in the juxta-membrane region; 95 2 STOP = human IGF-I receptor subunit having a truncated beta subunit; 957 Ala = human IGF-I receptor subunit with alanine substitution at residue 957 in the juxta-membrane region; 1003 Ala = human IGF-I receptor subunit with alanine substitution at residue 1003 in the ATP binding domain; Δ22 = human IGF-I receptor subunit with 22 amino acid deletion at residues 943 through 966; and IGFIR-CRH = human IGF-I receptor subunit having three additional amino acids (Cys- Arg-His) inserted at residue 950. All plasmids were purified on two cesium chloride gradients. EXAMPLE III Transfection of GC Rat Pituitary Cells and Rat I Fibroblasts GC rat pituitary cells (GC cells) secreting growth hormone were obtained from Dr. H. H. Samuels, New York, New York, but may be obtained from a variety of commercially available sources. GC rat pituitary cells were grown at 37° C in a humidified atmosphere of 95% air/5% C0 2 in Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 10% (vol/vol) fetal calf serum. Rat I fibroblasts were obtained from P. Koeffler (Cedars-Sinai Medical Center, Los Angeles CA) , but may be obtained from a variety of commercially available sources. Rat I fibroblast were grown at 37° C in αMEM supplemented with 10% (vol/vol) fetal calf serum. Semiconfluent GC cells or Rat I fibroblasts were cotransfected for 24 hours with 10 μg of linearized vector pRSV-IGFIR or pRSV-rlGFIR (plasmid mutants described in Example II; Rat I fibroblasts were only transfected with WT or 952 STOP and 1 μg pSV2neo to allow for neomycin-resistant selection (described by Southern P.J. et al., in J. Mol. Appl. Genet.. 1:327-341 (1982). Transfections were performed by the calcium phosphate coprecipitation method, as described by Prager, D. et al., J. Biol. Chem. 263:16580-16585 (1988). Cells were then split 1:6 and neomycin (G418; Gibco, Gaithersburg, MD) was added in fresh medium at a concentration of 400 μg/ml to GC cells and 600 μg/ml to Rat I fibroblasts. Medium was replenished every 72 hours. G418-resistant colonies were subcloned and further characterized. Mock transfected Rat I cells (I51Neo i.e., human IGF-I receptor cDNA and pSV2neo integrated) having no expression of human IGF-I receptor on the cell surface were utilized as controls. EXAMPLE IV Variant IGF-I Receptors Bind IGF-I Binding of radiolabeled IGF-I was performed in suspension. About 1 x IO 6 transfected GC cells or Rat I fibroblasts were incubated with [ 125 I]IGF-I (50,000 cpm, specific activity 2,000 Ci/mmol) (Amersham, Arlington Heights, IL) . Increasing concentrations of unlabeled recombinant human IGF-I (Met-59) (Fujisawa Pharmaceuticals Co., Osaka, Japan) in a final volume of 1 ml binding buffer (50 mM HEPES (pH 8) containing 1% bovine serum albumin, 120mM or 150 mM NaCl, 1.2 M MgSO at about 15°C were added. Non-specific binding was defined as binding observed in the presence of excess (100 nM) unlabeled IGF-I. After 3 hours incubation, transfectants were centrifuged and cell-associated radioactivity was separated from free [ 125 I]IGF-I by adding 300 μl of ice- cold dibutylphthalate. Cell-associated radioactivity of the samples was then determined by gamma-counting. Calculation of total bound ligand included the free- labeled ligand. Increasing amounts of unlabeled IGF-I displaced GC cell-associated [ 125 I]IGF-I binding to all transfectants, with 50% displacement of maximum binding achieved by 0.6-2nM IGF-I. When these binding displacement data were subjected to Scatchard analysis, a linear plot was obtained for all mutant transfectants, indicating the presence of a single class of high affinity receptors in these GC transfectants. The derived association constant (Kd) for [ 125 I]IGF-I binding was similar in all transfectants, ranging from 0.25 to 0.66 nM, except for 940 Ala which had 1.19 nM Kd. This similarity of ligand affinity for the different mutant receptors is expected, because the configuration of the extracellular alpha subunit is expected to remain intact when the beta subunit was mutated. The derived number of variant IGF-I receptors present on each transfectant was increased from 7- to 34-fold compared to untransfected cells. Likewise, Scatchard analysis of the transfected Rat I fibroblast clones selected for further study revealed that although binding affinities for the intact human IGF-I receptor WT cDNA transfectants and truncated human IGF-I receptor cDNA transfectants 952 (STOP) (1.08 and 0.67nM, respectively) were similar to the Kd for IGF- I binding to untransfected Rat 1 fibroblasts, transfectants exhibited a 2.5 - 7 fold increase in IGF-I binding sites/cell. In summary, expression of variant human IGF-I receptor subunit cDNA in GC cells and Rat I fibroblasts results in an increase in IGF-I binding sites per cell. The increase in binding sites is attributable to the formation of variant IGF-I receptors. Example V Integration of Variant DNA Into Host Genome To confirm integration of exogenous human IGF-I receptor DNA into GC cell and Rat I fibroblast genomic DNA, Southern blot analysis of transfected cell DNA was performed. Genomic DNA isolated from transfected and untransfected cells was prepared as described by Prager, D. et al., J. Clin. Invest.. 85:1680-1685 (1990) and digested with BamHl or EcoRI (Bethesda Research Laboratories, Gaithersburg, MD) . The DNA fragments were separated by electrophoresis on an 0.8% agarose gel and transferred to a nylon membrane. Membranes were baked at 80°C for 2 hours and prehybridized at 65°C for 2 hours in 10 ml, 250 mM NaHPO„»H 2 0, 250 mM Na 2 HP0 4 -7H 2 0, 7% sodium dodecyl sulfate (SDS) , 1% BSA, and 1 mM EDTA. 32 P-Labeled IGF-I receptor cDNA (Boehringer Mannheim, Indianapolis, IN) with a specific activity of 6xl0 7 dpm was prepared by random priming. Hybridization was carried out at 65°C for 24 hours. Membrane was washed twice for 15 minutes in 200 ml, 2 x SSC (20 x SSC = 3 M sodium chloride and 0.3 M sodium citrate) and 0.1% SDS at 65°C, followed by washing twice in 200 ml, 0.2 x SSC-0.1% SDS for 15 min at 65°C. Filters were autoradiographed for 7 days at -70°C, using Kodak film (Eastman Kodak, Rochester, NY) and intensifying screens. The human receptor probe hybridized appropriately to all transfectant DNA samples but only hybridized minimally to DNA extracted from untransfected GC cells and Rat I fibroblasts, confirming that the exogenous human IGF-I receptor cDNAs were integrated into genomic DNA of these cells. The major -5 kilobase DNA fragment which was expected to be released from pRSV- IGFIR by digestion with EcoRI was visualized in each transfectant, in addition to randomly sized DNA bands. EXAMPLE VI Characterization of Variant IGF-I Receptor Variant IGF-I receptor formation (endogenous rat IGF-I receptor subunit/variant human IGF-I receptor subunit and/or variant human IGF-I receptor subunit/variant human IGF-I receptor subunit) was demonstrated by metabolically labeling transfectants with translabeled 35 S-methionine (ICN, Irvine, California) and then i munoprecipitating the proteins with both ocIR3 (Oncogene, Manhesset, NY) and Ab 1-2 monoclonal antibody obtained from Dr. K. Siddle, University of Cambridge, Cambridge, England. Confluent GC cells and Rat I fibroblast cells transfected with WT IGF-I receptor cDNA and 952 STOP IGF-I receptor cDNA cells were rinsed with 5 ml phosphate- buffered saline (PBS) and metabolically labeled at 37°C with 0.5 mCi [ 35 S]methionine (CSA, 1,049 ci/mmol) in 5 ml serum-free methionine-free medium. After 16 hours, the cells were lysed with lysis buffer (0.01 M NaCl, 0.5% deoxycholate, 1% Triton X-100, 0.1% SDS, 0.01% sodium azide, and ImM phenylmethylsulfonyl fluoride) and centrifuged at 3,000 rpm for 15 minutes at 4°C. Either oiR3 or Ab 1-2 were used at 1:500 or a 1:300 final concentration, respectively. Immune complexes were precipitated with protein A-Sepharose (Pharmacia Inc. , Piscataway, NJ) . The pellets were then washed and loaded onto 4% nondenaturing polyacrylamide SDS gels along with prestaining protein molecular weight markers (Bethesda Research Laboratories, Gaitherburg, MD) . cxIR3 recognizes the alpha subunit of human IGF- I receptor. Thus, the 460-kD WT receptor holotetramer and the truncated 300-kD 952 STOP variant receptor holotetramer appear as distinct bands on the gel in response to immunoprecipitation with xIR3. Ab 1-2 recognizes a carboxy terminal beta-subunit epitope of both rat and human IGF-I receptor, and therefore identifies the 360 kD variant (rat IGF-I receptor subunit/variant human IGF-I receptor subunit) receptor heterotetramer as a distinct band on the gel. The intact human IGF-I receptor holotetramer was immunoprecipitated by both αIR3 and Ab 1-2 in WT transfectants. lR3 precipitated the variant truncated- human receptor holotetramer in 952 STOP transfectants. The only predominant band in response to immunoprecipitation of 952 STOP transfectants with Ab 1-2 was the 360 kD variant rat/human hybrid receptor. EXAMPLE VII Longevity of Variant IGF-I Receptors To study the IGF-I receptor biosynthetic half- life, semiconfluent GC cell transfectants were metabolically labeled with [ 35 S]methionine as in Example VI. After 16 hours, medium was replenished with serum- free defined (SFD) medium containing methionine with or without 6.5 nM IGF-I. After further incubation at 37°C, the cells were harvested at 0, 0.5, 2, 6 and 16 hours and processed as described in Example VI. Half-life of WT receptors was greater than 6 hours. Denεitometric scanning revealed a 90% increase in receptor degradation by 16 hours. The addition of ligand appeared not to have influenced the rate of degradation of the receptors. In 952 STOP transfectants, variant rat/human hybrid receptor degradation rates were clearly slower, and by 16 hours the majority of synthesized receptors were still present. Similarly, the presence of ligand did not affect the variant rat/human hybrid receptor half-life. Variant truncated-human IGF-I holotetramers also appeared to degrade at a slower rate, similar to the slow degradation of variant rat/human hybrid receptors. EXAMPLE VIII IGF-I Internalization About lxlO 6 Rat I fibroblast and GC cell transfectants were incubated with [ 125 I]IGF-I (40-50,000 cpm) in 0.5 ml DMEM (pH 7.8) containing 1% bovine serum albumin and 10 mM HEPES for 30 minutes at 37°C. At the end of the indicated incubation period, the medium was acidified by addition of 30 μl IN HCl and allowed to incubate at 4°C for an additional 6 minutes. Intracellular (acid-resistant) or cell-associated [ 125 I]IGF-I was determined as described in Example VI. Degraded [ 125 I]IGF-I was assessed by trichloroacetic acid precipitation (10%) of 300 μl of incubation buffer. After 4 more minutes at 4°C, the degraded [ 125 I]IGF-I in the supernatant was determined by gamma counting as described in Levy J.R., et al. Endocrinology, 119:572- 579 (1986) . Percent internalization is calculated by the following equation: intracellular + degraded x 100 surface + intracellular + degraded after subtraction of respective values for untransfected cells. GC cells transfected with cDNA having amino acid substitutions at positions 940, 943 or 950 and IGFIR-CRH transfectants, as well as the WT transfectants, internalized 46-70% of exogenous [ 125 I]IGF-I. In contrast, the 957 Ala transfectant only internalized 24% total bound [ 125 I]IGF-I and the Δ22 and the 1003 Ala transfectants failed to internalize labeled IGF-I ligand. Similarly, both untransfected Rat 1 fibroblasts and WT transfectants internalized [ 125 I]IGF-I in a time dependent manner. However, 952 STOP transfectants failed to internalize labeled ligand during a 30 minute incubation period. These internalization studies, considered in light of the results of the immunoprecitation assays of Example VI, reveal that the variant IGF-I receptor subunits produced from amino acid substitutions at residue 957 and 1003 and deletion mutations, complex with endogenous IGF-I receptor subunits of the Rat I fibroblast and GC cells, forming variant rat/human hybrid IGF-I receptors. These variant IGF-I receptors exert a negative trans-dominant effect on endogenous IGF-I receptor ligand internalization. EXAMPLE IX Variant IGF-I Receptor Autophosphorylation and Phosphorylation of Endogenous Substrate Transfectant GC cells labeled for 10 or 16 hours with [ 35 S]methionine were washed with PBS and incubated with or without IGF-I (6.5nM) in serum-free defined medium for 1 minute at 37°C. Cells were then lysed with lysis buffer (1% Triton X-100, 30 mM sodium pyrophosphate, 10 mM Tris (pH 7.6), 5 mM EDTA (pH 8), 50 mM NaCl, 0.1% bovine serum albumin, 2 mM sodium orthovanadate, 200 mM phenylmethylsulfonyl fluoride) and centrifuged for 15 minutes at 3000 rpm. Immunoprecipitation was performed using a monoclonal anti-phosphotyrosine antibody, either Ab 2 or PY 20, at 4°C for 3 or 16 hours, respectively. (Ab 2 obtained from Oncogene Science, Manhasset, NY. PY 20 obtained from ICN, Costa Mesa, CA.) Protein A-Sepharose with anti-mouse IgG (Sigma Chemical Corp., St. Louis, Missouri) for assays performed with Ab 1-2 and without anti-mouse IgG for assays performed with PY 20 was incubated with the monoclonal anti-phosphotyrosine antibody cell lysate complex for 2 hours at room temperature. Immunoprecipitates were washed six times in 0.9 ml lysis buffer, resuspended in 0.04 ml sample buffer, heated to 95°C for 3-5 minutes, and electrophoresed on 7.5% sodium dodecyl sulfate- polyacrylamide gels. In response to IGF-I ligand, WT and 57 Ala transfectants induced tyrosine phosphorylation of both the beta subunit of the IGF-I receptor (97kD) and cytoplasmic protein substrates containing tyrosine residues, ppl85 and/or IRS-1 (165-185 kD) . The 950 Ala transfectants failed to phosphorylate IRS-1 but otherwise demonstrated similar phosphorylation to the WT transfectants, albeit of lesser intensity. The 943 Ala transfectants autophosphorylated the beta subunit of the receptor but the phosphorylation of IRS-1 was reduced as compared to WT transfectants. The 1003 Ala and 952 STOP transfectants failed to undergo ligand-mediated IGF-I receptor autophosphorylation and endogenous protein phosphorylation. These results suggest that the tyrosine residues at positions 950 and possibly 943 are important sites for IRS-1 phosphorylation, and that IRS-1 may mediate IGF-I ligand signaling to the growth hormone gene. Moreover, the level of growth hormone suppression approximately parallels the IGF-I stimulated tyrosine kinase activity in cells as assessed by tyrosine phosphorylation of the IGF-I receptor substrate, IRS-1. The lysine residue at position 1003 in the ATP domain is critical for autophosphorylation and phosphorylation. EXAMPLE X Variant IGF-I Receptors Inhibit IGF-I Signaling To determine the effect of variant IGF-I receptor formation on endogenous rat IGF-I receptor ability to transduce the IGF-I signal to the growth hormone gene, approximately 5xl0 5 GC cells were plated on 9-cm 2 multiwells and grown for 24 hours in growth medium. The medium was then aspirated and replenished with 1.5- 2.0 ml Yamasaki, H. , et al., Endocrinology. 128: 857-862 (1991) (0.6 nM triiodothyronine (T 3 ) , 0.2 ng/ml ( parathyroid hormone (PTH), lOmg/ml transferrin, 0.1 ng/ml epidermal growth factor, 0.2 ng/nl fibroblast growth factor, 10 pg/ml glucagon, 100 nM hydrocortisone, and 0.3% bovine serum albumin in DMEM) with or without 6.5 nM IGF-I. Aliquots of medium were removed at various time intervals and assayed for rat growth hormone using radiolabeled rat growth hormone and anti-rat growth hormone antibody supplied by the National Hormone and Pituitary Program, National Institute of Diabetes and Digestive and Kidney Diseases (Bethesda, MD) . Percent growth hormone secretion suppression was calculated by the following formula: (GH secreted from UC - GH secreted from TO x 100 GH secreted from UC where GH is growth hormone, UC is untreated cells and TC is treated cells. After 18 hours of IGF-I treatment, untransfected cells only suppressed growth hormone by 20%, whereas WT transfectants already exhibited a 58% suppression of growth hormone secretion. Both the 90 Ala and 957 Ala point mutations showed enhanced IGF-I suppression of growth hormone, similar to that observed in the WT transfectants. The 943 Ala point mutation showed a suppressive effect intermediate between IGF-I action in WT and untransfected cells. The transfectants with amino acid substitutions at residue 950 or 1003 responded to IGF-I similarly to untransfected cells. The 952 STOP failed to suppress growth hormone secretion. By 36 hours, untransfected cells showed a 40% suppression of growth hormone, and WT transfectants a 60% suppression of growth hormone. However, 952 STOP cells still failed to respond to the IGF-I ligand and in fact, growth hormone secretion was higher in these cells than in nontransfected control cells despite the presence of endogenous IGF-I receptors. The 952 STOP transfectants were therefore completely devoid of biological signaling to growth hormone despite the presence of endogenous rat IGF-I receptors. These observations suggest that of the three tyrosine residues localized in the juxta-membrane domain of the human IGF-I receptor, the tyrosine residue at position 950 is critical for the IGF-I signaling to the growth hormone gene, while the tyrosine at position 957 does not appear to be required. The reduced efficiency with which the 943 Ala suppressed growth hormone in response to IGF-I suggests the possibility that the tyrosine at position 943 may be an important folding and/or contact point for protein(s) involved in the signaling cascade to the growth hormone gene in the somatotroph nucleus. Clearly, the 952 ST0P IGF-I receptor subunit behaves as a dominant negative inhibitor of endogenous IGF-I receptor function. EXAMPLE XI Variant IGF-I Receptors Modify IGF-I Mediated Cell Proliferation To further demonstrate that variant IGF-I receptor formation modifies endogenous receptor function, cellular proliferation in the presence and absence of IGF-I was studied by seeding about lxlO 4 Rat I fibroblast WT and 952 STOP transfectants in SFD medium for 24 hrs. Medium was then replenished and a concentration of 3.25 nM IGF-I was added to the "IGF-I Present" test wells. After 72 hours incubation, medium was aspirated and the monolayer washed twice with 5 ml PBS (pH 7.4). lOOμl of crystal violet (Sigma Chemical Co. , St. Louis, MO) made up to 0.5% in methanol at room temperature was added to each well for 15 minutes. The wells were then destained with 1 ml H 2 0 and allowed to air dry. The crystals were then dissolved in 100 μl 0.1 M sodium citrate (pH 4.2) and 50% ethanol for 30 minutes at room temperature. Plates were read on Elisa plate reader at 540 nM wavelength. Growth stimulatory ratios (% GSR) were calculated as follows: % GSR = A 5ample - A blan , X 100 " A • control — "Λblank Where A=absorbance. Data were corrected for mock transfected cells (I51Neo) by subtracting out the I51Neo values. Table 1 provides the growth stimulatory ratio for WT and 952 STOP transfectants in the presence and absence of IGF-I, measured as a percent of cell proliferation of control transfected cells. Table 1 Growth Stimulatory Ratio IGF-I IGF-I Present Transfectant Absent (3.25nM. WT 100+10 300+20 952 STOp *70+5 *80+l WT transfectants grew faster than 952 STOP transfectants (p-0.005) both in the absence and presence of IGF-I ligand. 952 STOP transfectants did not respond to IGF-I. EXAMPLE XII Variant IGF-I Receptors Modify IGF-I Mediated DNA Synthesis The blunted growth response of the variant IGF- I receptor transfectants identified in Example XII was confirmed by measuring DNA synthesis by [ 3 H]thymidine uptake after IGF-I treatment. About lxlO 4 Rat I fibroblast, WT or 952 STOP transfectants were grown in SFD medium for 24 hours. Medium was then replenished and 2 ml concentration of 3.25 nM IGF-I was added to the "IGF-I Present" test wells. After 48 hours incubation, [ 3 H]thymidine (1 μCi) (ICN Biochemicals, Costa Mesa, CA) was added to the medium and the cells were allowed to incubate at 37°C for 5 hours. Medium was then aspirated and 100 μl of cold tricarboxylic acid (10%) was added to each well for 20 minutes at 4°C. Following aspiration the wells were washed twice with 10% tricarboxylic acid. 100 μl of IN sodium hydroxide was then added to each well and the plates incubated on a shaker for 15-30 minutes at room temperatures. Following solubilization, 90μl was removed from each well for counting in a liquid scintillation counter. The results were corrected by subtracting values for control transfected I51Neo cells. The values presented in Table 2 represent the mean of six determinations. Table 2 r 3 H " 1Thymidine Incorporation Into Transfectants IGF-I IGF-I Present Transfectant Absent (3.25nM, WT 165±6 **323+9 952 STOp *57± 2 .7 *55+2.4 *p<0.005, WT vs. 52 STOP. **p<0.005, IGF-I vs. no IGF-I. [ 3 H]thymidine incorporation into WT transfectants more than doubled in the presence of IGF-I. IGF-I, however, did not stimulate DNA synthesis in 952 STOP transfectants. Furthermore, the absolute growth rate of 952 STOP transfectants was markedly lower than that of WT or untransfected Rat 1 fibroblasts. These results demonstrate that IGF-I is a positive growth regulator operating through intact endogenous IGF-I receptors of Rat I fibroblasts and that overexpression of variant IGF- I receptor cDNA can be used to modify this positive growth regulation. EXAMPLE XIII Variant IGF-I Receptors Alter Cell Morphology and Inhibit Colony Formation About 1x10 s untranfected Rat I fibroblasts, WT transfectants or 952 STOP transfectants were each plated in SFD medium. A concentration of 50 nM IGF-I or 650 nM insulin was added to test plates and all plates were allowed to incubate for 48 hours. WT transfectants exhibited a marked change in cell morphology after treatment with either IGF-I or insulin. Transfectants grown in the absence of ligand had a normal phenotypic appearance similar to that of untransfected Rat 1 fibroblasts and 952 STOP transfectants. In the presence of IGF-I or insulin, however, WT transfectants rounded up and became loosely adherent to the plate. Neither the untransfected Rat 1 fibroblast nor the 952 STOP transfectants exhibited a significant change in cellular morphology following ligand addition. IGF-I is >10-fold more potent than insulin in promoting this altered morphology and exhibits 10 times the affinity for binding IGF-I receptor than insulin. These observations indicate that these growth factor mediated phenotypic changes occur through the overexpressed IGF-I receptor which can be modified by the presence of variant IGF-I receptor. To determine whether changes in colony morphology implied a more universal change in the growth phenotype of transfectants, their growth in soft agar was analyzed. About 2xl0 3 untransfected Rat I fibroblast, WT transfectants or 952 STOP transfectants were plated in groups of 6 in 35 mm 0.3% soft agar containing 0.42 ml, 0.3% Bacto-Agar, 0.83 ml αMEM, 0.33 ml, 10% fetal calf serum, 0.2 ml penicillin and streptomycin combined, in the absence or presence of 13 nM IGF-I. Plates were incubated at 37° C for 12 days. All colonies containing >40 cells were scored. The figures in Table 3 represent the mean number of colonies counted in six wells. Table 3. Colony Formation in Soft Agar IGF-I IGF-I Present Transfectant Absent (13nM) Untransfected 21.8+5.3 37.5+7.5 WT *46.2±9.1 *65.5+3.4 952 STOP 0.7 1.8 *p<0.001, vs. untransfected Rat I fibroblast. Untransfected Rat 1 fibroblast grew in soft agar, but their colony size was much smaller than that of WT transfectants. The small untransfected Rat 1 fibroblast colonies increased in size and number in response to IGF- I, but were still fewer and smaller in size than the WT colonies in the absence of IGF-I. After ligand treatment, WT colonies increased both in size and number. In contrast, 952 STOP transfectants failed to grow in soft agar in the absence of ligand and showed only minimal growth in the presence of ligand. Thus, the endogenous rat IGF-I receptors were unable to promote anchorage-independent growth of 952 STOP transfectants, suggesting that expression of variant IGF- I subunits results in the formation of non-functional variant receptors. EXAMPLE XIV Variant IGF-I Receptors Inhibit In Vivo Tumorigenicity To determine if variant receptors exerted a dominant-negative phenotypic effect in vivo, three groups of nine athymic nude mice were injected subcutaneously over the right or left flank with about 1x10 s untransfected Rat I fibroblasts, WT transfectants or 952 STOP transfectants. Mice were observed for eight weeks prior to sacrifice. All the mice injected with WT transfectants developed palpable and visible tumors within three weeks of injection. Six of nine mice injected with untransfected Rat 1 fibroblasts developed tumors only after 5-6 weeks. Mice injected with WT transfectants developed large tumors as compared to those in mice injected with untransfected Rat l fibroblasts which were smaller and necrotic. None of the mice injected with 952 STOP transfectants developed tumors during the 8 week monitoring period. Following sacrifice, solid tumors resulting from Rat 1 fibroblast (Rat I MT) and WT transfectants (WT MT1-9) were enzymatically dispersed with collagenase (0.35%) and hyaluronidase (0.1%) and cultured in vitro in G418. Both native as well as ex vivo Rat I MT cells failed to grow in the presence of genticin. However, all the WT MT1-9 cells derived ex vivo proliferated j vitro in G418 at 600 μg/ml. Specific [ 125 I]-IGF-I binding to these cells, performed as described in Example IV, demonstrated that the ex vivo WT MT1-9 cells continued to overexpress IGF-I receptors (20-41% specific IGF-I binding) , as compared to untransfected Rat I fibroblasts or Rat I MT cells (5% specific IGF-I binding) . Southern blot analysis carried out as described in Example V on EcoRl digested DNA from Rat I MT and WT Ml-9 tumor derived cells, confirmed that the variant IGF- I receptor was still integrated into the ex vivo cells. Pathological examination of the WT M4 and Rat I MT formalin fixed tumors revealed that the tumors contained vimentin immunoreactivity consistent with sarcoma differentiation. They did not express keratin, S100 protein, neurofila ents, leukocyte common antigen, desmin or yoglobin, thus excluding carcinomas, neural differentiation, lymphoma or muscle differentiation. Electron microscopy was consistent with sarcomatous differentiation. Both tumors were fibrosarcomas, with the Rat I MT tumors having large areas of necrosis consistent with the more friable nature of this tumor, compared to the Rat WT M4 tumor which was extremely hard, and had few areas of necrosis. Although the invention has been described with reference to presently preferred embodiments, it should be understood that various modifications can be made without departing from the spirit of the invention. SEQUENCE LISTING (1) GENERAL INFORMATION: (i) APPLICANT: Prager, Diane Melmed, Shlomo (ii) TITLE OF INVENTION: VARIANT INSULIN-LIKE GROWTH FACTOR I RECEPTOR SUBUNITS AND METHODS FOR USE THEREOF (iii) NUMBER OF SEQUENCES: 14 (iv) CORRESPONDENCE ADDRESS: (A) ADDRESSEE: Pretty, Schroeder, Brueggemann & Clark (B) STREET: 444 South Flower Street, Suite 2000 (C) CITY: Los Angeles (D) STATE: California (E) COUNTRY: U.S.A. (F) ZIP: 90071 (v) COMPUTER READABLE FORM: (A) MEDIUM TYPE: Floppy disk (B) COMPUTER: IBM PC compatible (C) OPERATING SYSTEM: PC-DOS/MS-DOS (D) SOFTWARE: Patentin Release #1.0, Version #1.25 (vi) CURRENT APPLICATION DATA: (A) APPLICATION NUMBER: US (B) FILING DATE: (C) CLASSIFICATION: (viii) ATTORNEY/AGENT INFORMATION: (A) NAME: Whiteford, Wendy A. (B) REGISTRATION NUMBER: P36,964 (C) REFERENCE/DOCKET NUMBER: P07 31076 (ix) TELECOMMUNICATION INFORMATION: (A) TELEPHONE: 213-622-7700 (B) TELEFAX: 213-489-4210 (2) INFORMATION FOR SEQ ID NO:l: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 4975 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: double (D) TOPOLOGY: both (ii) MOLECULE TYPE: cDNA (ix) FEATURE: (A) NAME/KEY: CDS (B) LOCATION: 32..4135 (D) OTHER INFORMATION: /product= "growth factor receptor signal peptide" (ix) FEATURE: (A) NAME/KEY: sig_peptide (B) LOCATION: 32..121 (ix) FEATURE: (A) NAME/KEY: mat_peptide (B) LOCATION: 122..2239 (D) OTHER INFORMATION: /product= "growth factor receptor alpha subunit" (ix) FEATURE: (A) NAME/KEY: mat_peptide (B) LOCATION: 2252..4132 (D) OTHER INFORMATION: /product= "growth factor receptor beta subunit" (xi) SEQUENCE DESCRIPTION: SEQ ID NO:l: GAGAAAGGGA ATTTCATCCC AAATAAAAGG A ATG AAG TCT GGC TCC GGA GGA 52 Met Lys Ser Gly Ser Gly Gly -30 -25 GGG TCC CCG ACC TCG CTG TGG GGG CTC CTG TTT CTC TCC GCC GCG CTC 100 Gly Ser Pro Thr Ser Leu Trp Gly Leu Leu Phe Leu Ser Ala Ala Leu -20 -15 -10 TCG CTC TGG CCG ACG AGT GGA GAA ATC TGC GGG CCA GGC ATC GAC ATC 148 Ser Leu Trp Pro Thr Ser Gly Glu lie Cys Gly Pro Gly lie Asp lie -5 1 5 CGC AAC GAC TAT CAG CAG CTG AAG CGC CTG GAG AAC TGC ACG GTG ATC 196 Arg Asn Asp Tyr Gin Gin Leu Lys Arg Leu Glu Asn Cys Thr Val lie 10 15 20 25 GAG GGC TAC CTC CAC ATC CTG CTC ATC TCC AAG GCC GAG GAC TAC CGC 244 Glu Gly Tyr Leu His lie Leu Leu lie Ser Lys Ala Glu Asp Tyr Arg 30 35 40 AGC TAC CGC TTC CCC AAG CTC ACG GTC ATT ACC GAG TAC TTG CTG CTG 292 Ser Tyr Arg Phe Pro Lys Leu Thr Val lie Thr Glu Tyr Leu Leu Leu 45 50 55 TTC CGA GTG GCT GGC CTC GAG AGC CTC GGA GAC CTC TTC CCC AAC CTC 340 Phe Arg Val Ala Gly Leu Glu Ser Leu Gly Asp Leu Phe Pro Asn Leu 60 65 70 ACG GTC ATC CGC GGC TGG AAA CTC TTC TAC AAC TAC GCC CTG GTC ATC 388 Thr Val lie Arg Gly Trp Lys Leu Phe Tyr Asn Tyr Ala Leu Val lie 75 80 85 TTC GAG ATG ACC AAT CTC AAG GAT ATT GGG CTT TAC AAC CTG AGG AAC 436 Phe Glu Met Thr Asn Leu Lys Asp lie Gly Leu Tyr Asn Leu Arg Asn 90 95 100 105 ATT ACT CGG GGG GCC ATC AGG ATT GAG AAA AAT GCT GAC CTC TGT TAC 484 lie Thr Arg Gly Ala lie Arg lie Glu Lys Asn Ala Asp Leu Cys Tyr 110 115 120 CTC TCC ACT GTG GAC TGG TCC CTG ATC CTG GAT GCG GTG TCC AAT AAC 532 Leu Ser Thr Val Asp Trp Ser Leu lie Leu Asp Ala Val Ser Asn Asn 125 130 135 TAC ATT GTG GGG AAT AAG CCC CCA AAG GAA TGT GGG GAC CTG TGT CCA 580 Tyr lie Val Gly Asn Lys Pro Pro Lys Glu Cys Gly Asp Leu Cys Pro 140 145 150 GGG ACC ATG GAG GAG AAG CCG ATG TGT GAG AAG ACC ACC ATC AAC AAT 628 Gly Thr Met Glu Glu Lys Pro Met Cys Glu Lys Thr Thr lie Asn Asn 155 160 165 GAG TAC AAC TAC CGC TGC TGG ACC ACA AAC CGC TGC CAG AAA ATG TGC 676 Glu Tyr Asn Tyr Arg Cys Trp Thr Thr Asn Arg Cys Gin Lys Met Cys 170 175 180 185 CCA AGC ACG TGT GGG AAG CGG GCG TGC ACC GAG AAC AAT GAG TGC TGC 724 Pro Ser Thr Cys Gly Lys Arg Ala Cys Thr Glu Asn Asn Glu Cys Cys 190 195 200 CAC CCC GAG TGC CTG GGC AGC TGC AGC GCG CCT GAC AAC GAC ACG GCC 772 His Pro Glu Cys Leu Gly Ser Cys Ser Ala Pro Asp Asn Asp Thr Ala 205 210 215 TGT GTA GCT TGC CGC CAC TAC TAC TAT GCC GGT GTC TGT GTG CCT GCC 820 Cys Val Ala Cys Arg His Tyr Tyr Tyr Ala Gly Val Cys Val Pro Ala 220 225 230 TGC CCG CCC AAC ACC TAC AGG TTT GAG GGC TGG CGC TGT GTG GAC CGT 868 Cys Pro Pro Asn Thr Tyr Arg Phe Glu Gly Trp Arg Cys Val Asp Arg 235 240 245 GAC TTC TGC GCC AAC ATC CTC AGC GCC GAG AGC AGC GAC TCC GAG GGG 916 Asp Phe Cys Ala Asn lie Leu Ser Ala Glu Ser Ser Asp Ser Glu Gly 250 255 260 265 TTT GTG ATC CAC GAC GGC GAG TGC ATG CAG GAG TGC CCC TCG GGC TTC 964 Phe Val lie His Asp Gly Glu Cys Met Gin Glu Cys Pro Ser Gly Phe 270 275 280 ATC CGC AAC GGC AGC CAG AGC ATG TAC TGC ATC CCT TGT GAA GGT CCT 1012 lie Arg Asn Gly Ser Gin Ser Met Tyr Cys lie Pro Cys Glu Gly Pro 285 290 295 TGC CCG AAG GTC TGT GAG GAA GAA AAG AAA ACA AAG ACC ATT GAT TCT 1060 Cys Pro Lys Val Cys Glu Glu Glu Lys Lys Thr Lys Thr lie Asp Ser 300 305 310 GTT ACT TCT GCT CAG ATG CTC CAA GGA TGC ACC ATC TTC AAG GGC AAT 1108 Val Thr Ser Ala Gin Met Leu Gin Gly Cys Thr lie Phe Lys Gly Asn 315 320 325 TTG CTC ATT AAC ATC CGA CGG GGG AAT AAC ATT GCT TCA GAG CTG GAG 1156 Leu Leu lie Asn lie Arg Arg Gly Asn Asn lie Ala Ser Glu Leu Glu 330 335 340 345 AAC TTC ATG GGG CTC ATC GAG GTG GTG ACG GGC TAC GTG AAG ATC CGC 1204 Asn Phe Met Gly Leu lie Glu Val Val Thr Gly Tyr Val Lys lie Arg 350 355 360 CAT TCT CAT GCC TTG GTC TCC TTG TCC TTC CTA AAA AAC CTT CGC CTC 1252 His Ser His Ala Leu Val Ser Leu Ser Phe Leu Lys Asn Leu Arg Leu 365 370 375 ATC CTA GGA GAG GAG CAG CTA GAA GGG AAT TAC TCC TTC TAC GTC CTC 1300 lie Leu Gly Glu Glu Gin Leu Glu Gly Asn Tyr Ser Phe Tyr Val Leu 380 385 390 GAC AAC CAG AAC TTG CAG CAA CTG TGG GAC TGG GAC CAC CGC AAC CTG 1348 Asp Asn Gin Asn Leu Gin Gin Leu Trp Asp Trp Asp His Arg Asn Leu 395 400 405 ACC ATC AAA GCA GGG AAA ATG TAC TTT GCT TTC AAT CCC AAA TTA TGT 1396 Thr lie Lys Ala Gly Lys Met Tyr Phe Ala Phe Asn Pro Lys Leu Cys 410 415 420 425 GTT TCC GAA ATT TAC CGC ATG GAG GAA GTG ACG GGG ACT AAA GGG CGC 1444 Val Ser Glu lie Tyr Arg Met Glu Glu Val Thr Gly Thr Lys Gly Arg 430 435 440 CAA AGC AAA GGG GAC ATA AAC ACC AGG AAC AAC GGG GAG AGA GCC TCC 1492 Gin Ser Lys Gly Asp lie Asn Thr Arg Asn Asn Gly Glu Arg Ala Ser 445 450 455 TGT GAA AGT GAC GTC CTG CAT TTC ACC TCC ACC ACC ACG TCG AAG AAT 1540 Cys Glu Ser Asp Val Leu His Phe Thr Ser Thr Thr Thr Ser Lys Asn 460 465 470 CGC ATC ATC ATA ACC TGG CAC CGG TAC CGG CCC CCT GAC TAC AGG GAT 1588 Arg lie He He Thr Trp His Arg Tyr Arg Pro Pro Asp Tyr Arg Asp 475 480 485 CTC ATC AGC TTC ACC GTT TAC TAC AAG GAA GCA CCC TTT AAG AAT GTC 1636 Leu He Ser Phe Thr Val Tyr Tyr Lys Glu Ala Pro Phe Lys Asn Val 490 495 500 505 ACA GAG TAT GAT GGG CAG GAT GCC TGC GGC TCC AAC AGC TGG AAC ATG 1684 Thr Glu Tyr Asp Gly Gin Asp Ala Cys Gly Ser Asn Ser Trp Asn Met 510 515 520 GTG GAC GTG GAC CTC CCG CCC AAC AAG GAC GTG GAG CCC GGC ATC TTA 1732 Val Asp Val Asp Leu Pro Pro Asn Lys Asp Val Glu Pro Gly He Leu 525 530 535 CTA CAT GGG CTG AAG CCC TGG ACT CAG TAC GCC GTT TAC GTC AAG GCT 1780 Leu His Gly Leu Lys Pro Trp Thr Gin Tyr Ala Val Tyr Val Lys Ala 540 545 550 GTG ACC CTC ACC ATG GTG GAG AAC GAC CAT ATC CGT GGG GCC AAG AGT 1828 Val Thr Leu Thr Met Val Glu Asn Asp His He Arg Gly Ala Lys Ser 555 560 565 GAG ATC TTG TAC ATT CGC ACC AAT GCT TCA GTT CCT TCC ATT CCC TTG 1876 Glu He Leu Tyr He Arg Thr Asn Ala Ser Val Pro Ser He Pro Leu 570 575 580 585 GAC GTT CTT TCA GCA TCG AAC TCC TCT TCT CAG TTA ATC GTG AAG TGG 1924 Asp Val Leu Ser Ala Ser Asn Ser Ser Ser Gin Leu He Val Lys Trp 590 595 600 AAC CCT CCC TCT CTG CCC AAC GGC AAC CTG AGT TAC TAC ATT GTG CGC 1972 Asn Pro Pro Ser Leu Pro Asn Gly Asn Leu Ser Tyr Tyr He Val Arg 605 610 615 TGG CAG CGG CAG CCT CAG GAC GGC TAC CTT TAC CGG CAC AAT TAC TGC 2020 Trp Gin Arg Gin Pro Gin Asp Gly Tyr Leu Tyr Arg His Asn Tyr Cys 620 625 630 TCC AAA GAC AAA ATC CCC ATC AGG AAG TAT GCC GAC GGC ACC ATC GAC 2068 Ser Lys Asp Lys He Pro He Arg Lys Tyr Ala Asp Gly Thr He Asp 635 640 645 ATT GAG GAG GTC ACA GAG AAC CCC AAG ACT GAG GTG TGT GGT GGG GAG 2116 He Glu Glu Val Thr Glu Asn Pro Lys Thr Glu Val Cys Gly Gly Glu 650 655 660 665 AAA GGG CCT TGC TGC GCC TGC CCC AAA ACT GAA GCC GAG AAG CAG GCC 2164 Lys Gly Pro Cys Cys Ala Cys Pro Lys Thr Glu Ala Glu Lys Gin Ala 670 675 680 GAG AAG GAG GAG GCT GAA TAC CGC AAA GTC TTT GAG AAT TTC CTG CAC 2212 Glu Lys Glu Glu Ala Glu Tyr Arg Lys Val Phe Glu Asn Phe Leu His 685 690 695 AAC TCC ATC TTC GTG CCC AGA CCT GAA AGG AAG CGG AGA GAT GTC ATG 2260 Asn Ser He Phe Val Pro Arg Pro Glu Arg Lys Arg Arg Asp Val Met 700 705 710 CAA GTG GCC AAC ACC ACC ATG TCC AGC CGA AGC AGG AAC ACC ACG GCC 2308 Gin Val Ala Asn Thr Thr Met Ser Ser Arg Ser Arg Asn Thr Thr Ala 715 720 725 GCA GAC ACC TAC AAC ATC ACC GAC CCG GAA GAG CTG GAG ACA GAG TAC 2356 Ala Asp Thr Tyr Asn He Thr Asp Pro Glu Glu Leu Glu Thr Glu Tyr 730 735 740 745 CCT TTC TTT GAG AGC AGA GTG GAT AAC AAG GAG AGA ACT GTC ATT TCT 2404 Pro Phe Phe Glu Ser Arg Val Asp Asn Lys Glu Arg Thr Val lie Ser 750 755 760 AAC CTT CGG CCT TTC ACA TTG TAC CGC ATC GAT ATC CAC AGC TGC AAC 2452 Asn Leu Arg Pro Phe Thr Leu Tyr Arg He Asp He His Ser Cys Asn 765 770 775 CAC GAG GCT GAG AAG CTG GGC TGC AGC GCC TCC AAC TTC GTC TTT GCA 2500 His Glu Ala Glu Lys Leu Gly Cys Ser Ala Ser Asn Phe Val Phe Ala 780 785 790 AGG ACT ATG CCC GCA GAA GGA GCA GAT GAC ATT CCT GGG CCA GTG ACC 2548 Arg Thr Met Pro Ala Glu Gly Ala Asp Asp He Pro Gly Pro Val Thr 795 800 805 TGG GAG CCA AGG CCT GAA AAC TCC ATC TTT TTA AAG TGG CCG GAA CCT 2596 Trp Glu Pro Arg Pro Glu Asn Ser He Phe Leu Lys Trp Pro Glu Pro 810 815 820 825 GAG AAT CCC AAT GGA TTG ATT CTA ATG TAT GAA ATA AAA TAC GGA TCA 2644 Glu Asn Pro Asn Gly Leu He Leu Met Tyr Glu He Lys Tyr Gly Ser 830 835 840 CAA GTT GAG GAT CAG CGA GAA TGT GTG TCC AGA CAG GAA TAC AGG AAG 2692 Gin Val Glu Asp Gin Arg Glu Cys Val Ser Arg Gin Glu Tyr Arg Lys 845 850 855 TAT GGA GGG GCC AAG CTA AAC CGG CTA AAC CCG GGG AAC TAC ACA GCC 2740 Tyr Gly Gly Ala Lys Leu Asn Arg Leu Asn Pro Gly Asn Tyr Thr Ala 860 865 870 CGG ATT CAG GCC ACA TCT CTC TCT GGG AAT GGG TCG TGG ACA GAT CCT 2788 Arg He Gin Ala Thr Ser Leu Ser Gly Asn Gly Ser Trp Thr Asp Pro 875 880 885 GTG TTC TTC TAT GTC CAG GCC AAA ACA GGA TAT GAA AAC TTC ATC CAT 2836 Val Phe Phe Tyr Val Gin Ala Lys Thr Gly Tyr Glu Asn Phe He His 890 895 900 905 CTG ATC ATC GCT CTG CCC GTC GCT GTC CTG TTG ATC GTG GGA GGG TTG 2884 Leu He He Ala Leu Pro Val Ala Val Leu Leu He Val Gly Gly Leu 910 915 920 GTG ATT ATG CTG TAC GTC TTC CAT AGA AAG AGA AAT AAC AGC AGG CTG 2932 Val He Met Leu Tyr Val Phe His Arg Lys Arg Asn Asn Ser Arg Leu 925 930 935 GGG AAT GGA GTG CTG TAT GCC TCT GTG AAC CCG GAG TAC TTC AGC GCT 2980 Gly Asn Gly Val Leu Tyr Ala Ser Val Asn Pro Glu Tyr Phe Ser Ala 940 945 950 GCT GAT GTG TAC GTT CCT GAT GAG TGG GAG GTG GCT CGG GAG AAG ATC 3028 Ala Asp Val Tyr Val Pro Asp Glu Trp Glu Val Ala Arg Glu Lys He 955 960 965 ACC ATG AGC CGG GAA CTT GGG CAG GGG TCG TTT GGG ATG GTC TAT GAA 3076 Thr Met Ser Arg Glu Leu Gly Gin Gly Ser Phe Gly Met Val Tyr Glu 970 975 980 985 GGA GTT GCC AAG GGT GTG GTG AAA GAT GAA CCT GAA ACC AGA GTG GCC 3124 Gly Val Ala Lys Gly Val Val Lys Asp Glu Pro Glu Thr Arg Val Ala 990 995 1000 ATT AAA ACA GTG AAC GAG GCC GCA AGC ATG CGT GAG AGG ATT GAG TTT 3172 He Lys Thr Val Asn Glu Ala Ala Ser Met Arg Glu Arg He Glu Phe 1005 1010 1015 CTC AAC GAA GCT TCT GTG ATG AAG GAG TTC AAT TGT CAC CAT GTG GTG 3220 Leu Asn Glu Ala Ser Val Met Lys Glu Phe Asn Cys His His Val Val 1020 1025 1030 CGA TTG CTG GGT GTG GTG TCC CAA GGC CAG CCA ACA CTG GTC ATC ATG 3268 Arg Leu Leu Gly Val Val Ser Gin Gly Gin Pro Thr Leu Val He Met 1035 1040 1045 GAA CTG ATG ACA CGG GGC GAT CTC AAA AGT TAT CTC CGG TCT CTG AGG 3316 Glu Leu Met Thr Arg Gly Asp Leu Lys Ser Tyr Leu Arg Ser Leu Arg 1050 1055 1060 1065 CCA GAA ATG GAG AAT AAT CCA GTC CTA GCA CCT CCA AGC CTG AGC AAG 3364 Pro Glu Met Glu Asn Asn Pro Val Leu Ala Pro Pro Ser Leu Ser Lys 1070 1075 1080 ATG ATT CAG ATG GCC GGA GAG ATT GCA GAC GGC ATG GCA TAC CTC AAC 3412 Met He Gin Met Ala Gly Glu He Ala Asp Gly Met Ala Tyr Leu Asn 1085 1090 1095 GCC AAT AAG TTC GTC CAC AGA GAC CTT GCT GCC CGG AAT TGC ATG GTA 3460 Ala Asn Lys Phe Val His Arg Asp Leu Ala Ala Arg Asn Cys Met Val 1100 1105 1110 GCC GAA GAT TTC ACA GTC AAA ATC GGA GAT TTT GGT ATG ACG CGA GAT 3508 Ala Glu Asp Phe Thr Val Lys He Gly Asp Phe Gly Met Thr Arg Asp 1115 1120 1125 ATC TAT GAG ACA GAC TAT TAC CGG AAA GGA GGC AAA GGG CTG CTG CCC 3556 He Tyr Glu Thr Asp Tyr Tyr Arg Lys Gly Gly Lys Gly Leu Leu Pro 1130 1135 1140 1145 GTG CGC TGG ATG TCT CCT GAG TCC CTC AAG GAT GGA GTC TTC ACC ACT 3604 Val Arg Trp Met Ser Pro Glu Ser Leu Lys Asp Gly Val Phe Thr Thr 1150 1155 1160 TAC TCG GAC GTC TGG TCC TTC GGG GTC GTC CTC TGG GAG ATC GCC ACA 3652 Tyr Ser Asp Val Trp Ser Phe Gly Val Val Leu Trp Glu He Ala Thr 1165 1170 1175 CTG GCC GAG CAG CCC TAC CAG GGC TTG TCC AAC GAG CAA GTC CTT CGC 3700 Leu Ala Glu Gin Pro Tyr Gin Gly Leu Ser Asn Glu Gin Val Leu Arg 1180 1185 1190 TTC GTC ATG GAG GGC GGC CTT CTG GAC AAG CCA GAC AAC TGT CCT GAC 3748 Phe Val Met Glu Gly Gly Leu Leu Asp Lys Pro Asp Asn Cys Pro Asp 1195 1200 1205 ATG CTG TTT GAA CTG ATG CGC ATG TGC TGG CAG TAT AAC CCC AAG ATG 3796 Met Leu Phe Glu Leu Met Arg Met Cys Trp Gin Tyr Asn Pro Lys Met 1210 1215 1220 1225 AGG CCT TCC TTC CTG GAG ATC ATC AGC AGC ATC AAA GAG GAG ATG GAG 3844 Arg Pro Ser Phe Leu Glu He He Ser Ser He Lys Glu Glu Met Glu 1230 1235 1240 CCT GGC TTC CGG GAG GTC TCC TTC TAC TAC AGC GAG GAG AAC AAG CTG 3892 Pro Gly Phe Arg Glu Val Ser Phe Tyr Tyr Ser Glu Glu Asn Lys Leu 1245 1250 1255 CCC GAG CCG GAG GAG CTG GAC CTG GAG CCA GAG AAC ATG GAG AGC GTC 3940 Pro Glu Pro Glu Glu Leu Asp Leu Glu Pro Glu Asn Met Glu Ser Val 1260 1265 1270 CCC CTG GAC CCC TCG GCC TCC TCG TCC TCC CTG CCA CTG CCC GAC AGA 3988 Pro Leu Asp Pro Ser Ala Ser Ser Ser Ser Leu Pro Leu Pro Asp Arg 1275 1280 1285 CAC TCA GGA CAC AAG GCC GAG AAC GGC CCC GGC CCT GGG GTG CTG GTC 4036 His Ser Gly His Lys Ala Glu Asn Gly Pro Gly Pro Gly Val Leu Val 1290 1295 1300 1305 CTC CGC GCC AGC TTC GAC GAG AGA CAG CCT TAC GCC CAC ATG AAC GGG 4084 Leu Arg Ala Ser Phe Asp Glu Arg Gin Pro Tyr Ala His Met Asn Gly 1310 1315 1320 GGC CGC AAG AAC GAG CGG GCC TTG CCG CTG CCC CAG TCT TCG ACC TGC 4132 Gly Arg Lys Asn Glu Arg Ala Leu Pro Leu Pro Gin Ser Ser Thr Cys 1325 1330 1335 TGATCCTTGG ATCCTGAATC TGTGCAAACA GTAACGTGTG CGCACGCGCA GCGGGGTGGG 4192 GGGGGAGAGA GAGTTTTAAC AATCCATTCA CAAGCCTCCT GTACCTCAGT GGATCTTCAG 4252 TTCTGCCCTT GCTGCCCGCG GGAGACAGCT TCTCTGCAGT AAAACACATT TGGGATGTTC 4312 CTTTTTTCAA TATGCAAGCA GCTTTTTATT CCCTGCCCAA ACCCTTAACT GACATGGGCC 4372 TTTAAGAACC TTAATGACAA CACTTAATAG CAACAGAGCA CTTGAGAACC AGTCTCCTCA 4432 CTCTGTCCCT GTCCTTCCCT GTTCTCCCTT TCTCTCTCCT CTCTGCTTCA TAACGGAAAA 4492 ATAATTGCCA CAAGTCCAGC TGGGAAGCCC TTTTTATCAG TTTGAGGAAG TGGCTGTCCC 4552 TGTGGCCCCA TCCAACCACT GTACACACCC GCCTGACACC GTGGGTCATT ACAAAAAAAC 4612 ACGTGGAGAT GGAAATTTTT ACCTTTATCT TTCACCTTTC TAGGGACATG AAATTTACAA 4672 AGGGCCATCG TTCATCCAAG GCTGTTACCA TTTTAACGCT GCCTAATTTT GCCAAAATCC 4732 TGAACTTTCT CCCTCATCGG CCCGGCGCTG ATTCCTCGTG TCCGGAGGCA TGGGTGAGCA 4792 TGGCAGCTGG TTGCTCCATT TGAGAGACAC GCTGGCGACA CACTCCGTCC ATCCGACTGC 4852 CCCTGCTGTG CTGCTCAAGG CCACAGGCAC ACAGGTCTCA TTGCTTCTGA CTAGATTATT 4912 ATTTGGGGGA ACTGGACACA ATAGGTCTTT CTCTCAGTGA AGGTGGGGAG AAGCTGAACC 4972 GGC 4975 (2) INFORMATION FOR SEQ ID NO:2: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 1367 amino acids (B) TYPE: amino acid (D) TOPOLOGY: linear (ii) MOLECULE TYPE: protein (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2: Met Lys Ser Gly Ser Gly Gly Gly Ser Pro Thr Ser Leu Trp Gly Leu -30 -25 -20 -15 Leu Phe Leu Ser Ala Ala Leu Ser Leu Trp Pro Thr Ser Gly Glu He -10 -5 1 Cys Gly Pro Gly He Asp He Arg Asn Asp Tyr Gin Gin Leu Lys Arg 5 10 15 Leu Glu Asn Cys Thr Val He Glu Gly Tyr Leu His He Leu Leu He 20 25 30 Ser Lys Ala Glu Asp Tyr Arg Ser Tyr Arg Phe Pro Lys Leu Thr Val 35 40 45 50 He Thr Glu Tyr Leu Leu Leu Phe Arg Val Ala Gly Leu Glu Ser Leu 55 60 65 Gly Asp Leu Phe Pro Asn Leu Thr Val He Arg Gly Trp Lys Leu Phe 70 75 80 Tyr Asn Tyr Ala Leu Val He Phe Glu Met Thr Asn Leu Lys Asp He 85 90 95 Gly Leu Tyr Asn Leu Arg Asn He Thr Arg Gly Ala He Arg He Glu 100 105 110 Lys Asn Ala Asp Leu Cys Tyr Leu Ser Thr Val Asp Trp Ser Leu He 115 120 125 130 Leu Asp Ala Val Ser Asn Asn Tyr He Val Gly Asn Lys Pro Pro Lys 135 140 145 Glu Cys Gly Asp Leu Cys Pro Gly Thr Met Glu Glu Lys Pro Met Cys 150 155 160 Glu Lys Thr Thr He Asn Asn Glu Tyr Asn Tyr Arg Cys Trp Thr Thr 165 170 175 Asn Arg Cys Gin Lys Met Cys Pro Ser Thr Cys Gly Lys Arg Ala Cys 180 185 190 Thr Glu Asn Asn Glu Cys Cys His Pro Glu Cys Leu Gly Ser Cys Ser 195 200 205 210 Ala Pro Asp Asn Asp Thr Ala Cys Val Ala Cys Arg His Tyr Tyr Tyr 215 220 225 Ala Gly Val Cys Val Pro Ala Cys Pro Pro Asn Thr Tyr Arg Phe Glu 230 235 240 Gly Trp Arg Cys Val Asp Arg Asp Phe Cys Ala Asn He Leu Ser Ala 245 250 255 Glu Ser Ser Asp Ser Glu Gly Phe Val He His Asp Gly Glu Cys Met 260 265 270 Gin Glu Cys Pro Ser Gly Phe He Arg Asn Gly Ser Gin Ser Met Tyr 275 280 285 290 Cys He Pro Cys Glu Gly Pro Cys Pro Lys Val Cys Glu Glu Glu Lys 295 300 305 Lys Thr Lys Thr He Asp Ser Val Thr Ser Ala Gin Met Leu Gin Gly 310 315 320 Cys Thr He Phe Lys Gly Asn Leu Leu He Asn He Arg Arg Gly Asn 325 330 335 Asn He Ala Ser Glu Leu Glu Asn Phe Met Gly Leu He Glu Val Val 340 345 350 Thr Gly Tyr Val Lys He Arg His Ser His Ala Leu Val Ser Leu Ser 355 360 365 370 Phe Leu Lys Asn Leu Arg Leu He Leu Gly Glu Glu Gin Leu Glu Gly 375 380 385 Asn Tyr Ser Phe Tyr Val Leu Asp Asn Gin Asn Leu Gin Gin Leu Trp 390 395 400 Asp Trp Asp His Arg Asn Leu Thr He Lys Ala Gly Lys Met Tyr Phe 405 ' 410 415 Ala Phe Asn Pro Lys Leu Cys Val Ser Glu He Tyr Arg Met Glu Glu 420 425 430 Val Thr Gly Thr Lys Gly Arg Gin Ser Lys Gly Asp He Asn Thr Arg 435 440 445 450 Asn Asn Gly Glu Arg Ala Ser Cys Glu Ser Asp Val Leu His Phe Thr 455 460 465 Ser Thr Thr Thr Ser Lys Asn Arg He He He Thr Trp His Arg Tyr 470 475 480 Arg Pro Pro Asp Tyr Arg Asp Leu He Ser Phe Thr Val Tyr Tyr Lys 485 490 495 Glu Ala Pro Phe Lys Asn Val Thr Glu Tyr Asp Gly Gin Asp Ala Cys 500 505 510 Gly Ser Asn Ser Trp Asn Met Val Asp Val Asp Leu Pro Pro Asn Lys 515 520 525 530 Asp Val Glu Pro Gly He Leu Leu His Gly Leu Lys Pro Trp Thr Gin 535 540 545 Tyr Ala Val Tyr Val Lys Ala Val Thr Leu Thr Met Val Glu Asn Asp 550 555 560 His He Arg Gly Ala Lys Ser Glu He Leu Tyr He Arg Thr Asn Ala 565 570 575 Ser Val Pro Ser He Pro Leu Asp Val Leu Ser Ala Ser Asn Ser Ser 580 585 590 Ser Gin Leu He Val Lys Trp Asn Pro Pro Ser Leu Pro Asn Gly Asn 595 600 605 610 Leu Ser Tyr Tyr He Val Arg Trp Gin Arg Gin Pro Gin Asp Gly Tyr 615 620 625 Leu Tyr Arg His Asn Tyr Cys Ser Lys Asp Lys He Pro He Arg Lys 630 635 640 Tyr Ala Asp Gly Thr He Asp He Glu Glu Val Thr Glu Asn Pro Lys 645 650 655 Thr Glu Val Cys Gly Gly Glu Lys Gly Pro Cys Cys Ala Cys Pro Lys 660 665 670 Thr Glu Ala Glu Lys Gin Ala Glu Lys Glu Glu Ala Glu Tyr Arg Lys 675 680 685 690 Val Phe Glu Asn Phe Leu His Asn Ser He Phe Val Pro Arg Pro Glu 695 700 705 Arg Lys Arg Arg Asp Val Met Gin Val Ala Asn Thr Thr Met Ser Ser 710 715 720 Arg Ser Arg Asn Thr Thr Ala Ala Asp Thr Tyr Asn He Thr Asp Pro 725 730 735 Glu Glu Leu Glu Thr Glu Tyr Pro Phe Phe Glu Ser Arg Val Asp Asn 740 745 750 Lys Glu Arg Thr Val He Ser Asn Leu Arg Pro Phe Thr Leu Tyr Arg 755 760 765 770 He Asp He His Ser Cys Asn His Glu Ala Glu Lys Leu Gly Cys Ser 775 780 785 Ala Ser Asn Phe Val Phe Ala Arg Thr Met Pro Ala Glu Gly Ala Asp 790 795 800 Asp He Pro Gly Pro Val Thr Trp Glu Pro Arg Pro Glu Asn Ser He 805 810 815 Phe Leu Lys Trp Pro Glu Pro Glu Asn Pro Asn Gly Leu He Leu Met 820 825 830 Tyr Glu He Lys Tyr Gly Ser Gin Val Glu Asp Gin Arg Glu Cys Val 835 840 845 850 Ser Arg Gin Glu Tyr Arg Lys Tyr Gly Gly Ala Lys Leu Asn Arg Leu 855 860 865 Asn Pro Gly Asn Tyr Thr Ala Arg He Gin Ala Thr Ser Leu Ser Gly 870 875 880 Asn Gly Ser Trp Thr Asp Pro Val Phe Phe Tyr Val Gin Ala Lys Thr 885 890 895 Gly Tyr Glu Asn Phe He His Leu He He Ala Leu Pro Val Ala Val 900 905 910 Leu Leu He Val Gly Gly Leu Val He Met Leu Tyr Val Phe His Arg 915 920 925 930 Lys Arg Asn Asn Ser Arg Leu Gly Asn Gly Val Leu Tyr Ala Ser Val 935 940 945 Asn Pro Glu Tyr Phe Ser Ala Ala Asp Val Tyr Val Pro Asp Glu Trp 950 955 960 Glu Val Ala Arg Glu Lys He Thr Met Ser Arg Glu Leu Gly Gin Gly 965 970 975 Ser Phe Gly Met Val Tyr Glu Gly Val Ala Lys Gly Val Val Lys Asp 980 985 990 Glu Pro Glu Thr Arg Val Ala He Lys Thr Val Asn Glu Ala Ala Ser 995 1000 1005 1010 Met Arg Glu Arg He Glu Phe Leu Asn Glu Ala Ser Val Met Lys Glu 1015 1020 1025 Phe Asn Cys His His Val Val Arg Leu Leu Gly Val Val Ser Gin Gly 1030 1035 1040 Gin Pro Thr Leu Val He Met Glu Leu Met Thr Arg Gly Asp Leu Lys 1045 1050 1055 Ser Tyr Leu Arg Ser Leu Arg Pro Glu Met Glu Asn Asn Pro Val Leu 1060 1065 1070 Ala Pro Pro Ser Leu Ser Lys Met He Gin Met Ala Gly Glu He Ala 1075 1080 1085 1090 Asp Gly Met Ala Tyr Leu Asn Ala Asn Lys Phe Val His Arg Asp Leu 1095 1100 1105 Ala Ala Arg Asn Cys Met Val Ala Glu Asp Phe Thr Val Lys He Gly 1110 1115 1120 Asp Phe Gly Met Thr Arg Asp He Tyr Glu Thr Asp Tyr Tyr Arg Lys 1125 1130 1135 Gly Gly Lys Gly Leu Leu Pro Val Arg Trp Met Ser Pro Glu Ser Leu 1140 1145 1150 Lys Asp Gly Val Phe Thr Thr Tyr Ser Asp Val Trp Ser Phe Gly Val 1155 1160 1165 1170 Val Leu Trp Glu He Ala Thr Leu Ala Glu Gin Pro Tyr Gin Gly Leu 1175 1180 1185 Ser Asn Glu Gin Val Leu Arg Phe Val Met Glu Gly Gly Leu Leu Asp 1190 1195 1200 Lys Pro Asp Asn Cys Pro Asp Met Leu Phe Glu Leu Met Arg Met Cys 1205 1210 1215 Trp Gin Tyr Asn Pro Lys Met Arg Pro Ser Phe Leu Glu He He Ser 1220 1225 1230 Ser He Lys Glu Glu Met Glu Pro Gly Phe Arg Glu Val Ser Phe Tyr 1235 1240 1245 1250 Tyr Ser Glu Glu Asn Lys Leu Pro Glu Pro Glu Glu Leu Asp Leu Glu 1255 1260 1265 Pro Glu Asn Met Glu Ser Val Pro Leu Asp Pro Ser Ala Ser Ser Ser 1270 1275 1280 Ser Leu Pro Leu Pro Asp Arg His Ser Gly His Lys Ala Glu Asn Gly 1285 1290 1295 Pro Gly Pro Gly Val Leu Val Leu Arg Ala Ser Phe Asp Glu Arg Gin 1300 1305 1310 Pro Tyr Ala His Met Asn Gly Gly Arg Lys Asn Glu Arg Ala Leu Pro 1315 1320 1325 1330 Leu Pro Gin Ser Ser Thr Cys 1335 (2) INFORMATION FOR SEQ ID NO:3: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3: CTGGGGAATG CTGTGCTGTA T 21 (2) INFORMATION FOR SEQ ID NO:4: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 24 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4: AATGGAGTGC TAGCTGCCTC TGTG 24 (2) INFORMATION FOR SEQ ID NO:5: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5: AACCCGGAGT GTTTCAGCGC T 21 (2) INFORMATION FOR SEQ ID NO:6: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6: AACCCGGAGT CATTCAGCGC T 21 (2) INFORMATION FOR SEQ ID NO:7: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7: AACCCGGAGG CTTTCAGCGC T 21 (2) INFORMATION FOR SEQ ID NO:8: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid , (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8: AACCCGGAGC TATTCAGCGC T 21 (2) INFORMATION FOR SEQ ID NO:9: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9: AACCCGGAGA CATTCAGCGC T 21 (2) INFORMATION FOR SEQ ID NO:10: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10: GCTGATGTGG CTGTTCCTGA T 21 (2) INFORMATION FOR SEQ ID NO:11: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 21 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:ll: GTGGCCATTG CTACAGTGAA C 21 (2) INFORMATION FOR SEQ ID NO:12: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 39 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12: GGGAATGGAG TGCTGTATCG GGAGAAGATC ACCATGAGC 39 (2) INFORMATION FOR SEQ ID NO:13: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 12 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13: TGCTCTAGAG CA 12 (2) INFORMATION FOR SEQ ID NO:14: (i) SEQUENCE CHARACTERISTICS: (A) LENGTH: 150 base pairs (B) TYPE: nucleic acid (C) STRANDEDNESS: single (D) TOPOLOGY: unknown (ii) MOLECULE TYPE: DNA (genomic) (xi) SEQUENCE DESCRIPTION: SEQ ID NO:14: GCAGGATGCC TGCGGCTCCA ACAGCTGGAA CATGGTGGAC GTGGACCTCC CGCCCAACAA 60 GGACGTGGAG CCCGGCATCT TACTACATGG GCTGAAGCCC TGGACTCAGT ACGCCGTTTA 120 CGTCAAGGCT GTGACCCTCA CCATGGTGGA 150

Claims: Claims : 1. A recombinant polynucleic acid comprising a sequence encoding IGF-I receptor subunit(s) characterized by modified IGF-I receptor function relative to the IGF-I receptor function of endogenous IGF-I receptor. 2. A recombinant polynucleic acid according to claim 1, wherein said IGF-I receptor function is tyrosine kinase activity. 3. A recombinant polynucleic acid according to claim 2 wherein said tyrosine kinase activity is autophosphorylation. 4. A recombinant polynucleic acid according to claim 2 wherein said tyrosine kinase activity is phosphorylation of cytoplasmic substrate. 5. A recombinant polynucleic acid according to claim 1 , wherein said sequence encodes a beta subunit of the IGF-I receptor. 6. A recombinant polynucleic acid according to claim 5, wherein said sequence further encodes an alpha subunit of the IGF-I receptor. 7. A recombinant polynucleic acid according to claim 2 encoding substantially the same amino acid sequence as residues 711 through about 929 of the sequence set forth in Sequence I.D. No. 2. 8. A recombinant polynucleic acid according to claim 1 encoding the amino acid sequence set forth in Sequence I.D. No. 2, wherein at least one amino acid residue of Sequence I.D. No. 2 is deleted or replaced with a residue which does not occur at the corresponding residue of said endogenous IGF-I subunit. 9. A recombinant polynucleic acid according to claim 8 encoding the amino acid sequence set forth in Sequence I.D. No. 2, wherein at least one of amino acid residues 943, 950, 957 or 1003 is replaced with a residue which does not occur at the corresponding residue of said endogenous IGF-I subunit. 10. A recombinant polynucleic acid according to claim 9, wherein amino acid residue 943 is alanine. 11. A recombinant polynucleic acid according to claim 9, wherein amino acid residue 950 is selected from cysteine, serine, alanine, leucine or threonine. 12. A recombinant polynucleic acid according to claim 9, wherein amino acid residue 957 is alanine. 13. A recombinant polynucleic acid according to claim 9, wherein amino acid residue 1003 is alanine. 14. A recombinant polynucleic acid according to claim 1 having substantially the same sequence as residues 2252 through 2909 of Sequence I.D. No. 1. 15. A recombinant polynucleic acid according to claim 1 comprising substantially the same sequence as Sequence I.D. No. 1, wherein at least one codon of Sequence I.D. No. 1 is deleted or replaced with a codon which does not occur at the corresponding residue of polynucleic acid encoding endogenous IGF-I receptor. 16. A recombinant polynucleic acid according to claim 15, wherein nucleotides 2977-2979 encode a stop codon. 17. A recombinant polynucleic acid according to claim 1, wherein said IGF-I receptor subunit is further characterized by its ability to complex with endogenous IGF-I receptor subunit(s) to form variant IGF-I receptor. 18. A vector containing a polynucleic acid of claim 1. 19. A cell containing a polynucleic acid according to claim 1. 20. A cell containing a vector according to claim 18. 21. A polypeptide comprising a sequence encoded by the polynucleic acid of claim 1. 22. An IGF-I receptor subunit encoded by the recombinant polynucleic acid of claim 8. 23. A variant IGF-I receptor subunit characterized by having modified IGF-I receptor function relative to the IGF-I receptor function of endogenous IGF-I receptor. 24. A variant IGF-I receptor subunit in accordance with claim 23, wherein said IGF-I receptor function is tyrosine kinase activity. 25. A variant IGF-I receptor subunit according to claim 23, wherein said variant receptor is further characterized by its ability to complex with endogenous IGF-I receptor subunit(s) to form variant IGF-I receptor. 26. An IGF-I receptor comprising the variant IGF-I receptor subunit of claim 23. 27. A method of inhibiting endogenous IGF-I receptor function, comprising contacting a cell with variant IGF-I receptor subunit under conditions suitable to form a variant IGF-I receptor, wherein said variant receptor is characterized by modified IGF-I receptor function relative to endogenous IGF-I receptor function. 28. A method in accordance with claim 25, wherein said cell is contacted with variant IGF-I receptor subunit by: (a) introducing a recombinant polynucleic acid encoding a variant IGF-I receptor subunit into said cell; (b) maintaining the product of step (a) under conditions suitable to allow expression of the variant IGF-I receptor subunit. 29. A method according to claim 28, wherein said recombinant polynucleic acid is cDNA. 30. A method according to claim 28, wherein said cell is a mammalian cell. 31. A method according to claim 30 wherein said mammalian cell is a human cell. 32. A method in accordance with claim 27, wherein said endogenous IGF-I receptor function is growth-factor dependent cell proliferation. 33. A method in accordance with claim 27, wherein said endogenous IGF-I receptor function is IGF-I receptor-mediated ligand-dependent cell transformation. 34. A method in accordance with claim 27, wherein said endogenous IGF-I receptor function is IGF-I receptor-mediated ligand-dependent cell tumorigenesis. 35. A method of making variant IGF-I receptor subunit, comprising: (a) mutagenizing the polynucleic acid sequence encoding the beta subunit of an IGF-I receptor to modify its IGF-I receptor function relative to endogenous IGF-I receptor function; (b) maintaining the product of step (a) under conditions suitable to allow expression of the variant IGF-I receptor subunit.

Inventors: MELDED SHLOMO, PRAGER DIANE, MELDED, SHLOMO, PRAGER, DIANE
Applicants: CEDARS SINAI MEDICAL CENTER, CEDARS-SINAI MEDICAL CENTER
Application year: 1994
Main classification: C12N15
IPC codes: A61K38, C07K14, C12N5, C12N15, C12P21, C12R1